In this work, a solution to monitor users’ activity within an indoor scenario is proposed. It is based on non-wearable and non-invasive sensing, and it is specially fitted for the elders’ home monitoring. The localization of a person is estimated through an optical sensing network that detects the floor vibration produced by the footstep when walking. Optical fiber Bragg sensors are integrated within high sensitive accelerometers to detect such vibration. Three similar accelerometers were developed from which sensitivities of 269 pm/G, 225 pm/G, and 209 pm/G were found. Allied to vibration detection, an algorithm is employed to retrieve one’s position from the data. In preliminary localization tests, the system has demonstrated an accuracy under 5 cm over a 3.2 m2 detection area, proving itself to be a promising solution for the targeted application.
A fiber Bragg gratings (FBGs) based system, constituted by six sensors, for wheelchair users muscle effort monitoring was proposed. Each sensor consists in one FBG embedded in epoxy resin, which was secured to Kinesio tape through a 3D printed connection system. After the approval of the Ethics and Deontology Committee and the Data Protection Officer of the University of Aveiro (Portugal), the sensors were implemented to evaluate wheelchair users muscle effort. The sensors were placed on the biceps, deltoids, and triceps (three sensors in each arm) of four wheelchairs users’ volunteers, which were asked to perform several exercises. The arms’ muscle effort required was estimated through the FBGs wavelength shift, which was related with the deformation of the epoxy resin during some of the wheelchair users’ daily movements: varying the typical used hand patterns on horizontal plane (pattern A, B and D); vertical and inclined dips; and going up and down a ramp. The results reveal that on the horizontal plane, the movement characterized by minor hand swings in relation to the wheelchair rim (pattern A), requires a smaller muscle effort, and the dips were the exercise requested to wheelchair users which demand the highest and most sudden muscle effort applied in the arms. The proposed system may be used to monitor and quantify the muscle effort related to any movement, aiding on the choice of techniques to promote the reduction of the muscle fatigue, and therefore contributing to the improvement of wheelchair user quality of life.
In this paper, the design and implementation of a cost-effective interrogation architecture, for dynamic strain monitoring of in-line Fabry-Perot interferometric (FPI) optical fiber sensors is presented. The common interrogation techniques for this type of sensors are based in the full spectrum analysis, which render them not adequate for dynamic/high frequency monitoring applications. In this work, we propose an alternative cost-effective solution, based on a simplified edge-filter technique, for the dynamic monitoring of FPI sensing devices. The FPI based sensor was produced from the recycling of optical fiber previously damaged by the catastrophic fuse effect using precise splicing techniques. A characterization was performed with two different devices, an optical spectrum analyzer (OSA) and the proposed device leading to similar behavior and sensitivity values.
Analysis of gait pattern of individuals is a very useful tool for the identification of locomotive motor anomalies, which can lead to early diagnosis and adequate treatment of patients with motor disorders. The knees are the lower limb joints exposed to major tension during human locomotion, presenting higher risk of a wider range of possible disorders. The devices used to monitor human joints should be comfortable and not restrain patients’ movement, while maintaining their resolution and accuracy. Most of current measurement techniques are based on electronic devices, which are often not adequate for demanding environments, such as the context of physical rehabilitation. We propose an e-Health sensing solution to dynamically monitor human knee angles during gait, using low-cost intrinsic Fabry-Perot interferometers optical fiber sensors (FPI-OFS). To the best of our knowledge, no previous efforts have reported the use of FPI sensors for such dynamic monitoring. The overall sensor consists of an optical fiber containing the FPI microcavity, which is embedded along the longitudinal direction of a kinesio tape (K-Tape), and placed along the knee rotation axis. Since the K-Tape has great adhesion to the skin, the FPI sensor is kept at the knee rotation axis, without restricting the user’s movements. During the knee flexion/extension, the K-Tape extends/compresses accordingly, resulting in the modulation of the reflected spectrum by the FPI-OFS. Several calibration and performance tests have been performed. Their results show the reliability and accuracy of the proposed solution, with sensibilities values of 53.8±2.4 pm/°.
Magnetic field sensors have been widely applied in several areas, for instance, in navigation, geophysical, aerospace engineering and biomedical research. The traditional methods used to sense this parameter have drawbacks related with size, stability, multiplexing capability, remote measurement and electromagnetic sensitivity. Due to the characteristics inherent to the optical fiber, including small dimensions, immunity to electromagnetic interference and the possibility of being used in hazardous environments, this technology has great potential for sensing different parameters. In this work, the magnetic field was monitored using a Fabry-Perot micro-cavity. The cavity, produced from the recycling of optical fiber previously destroyed by the catastrophic fuse effect, was filled with magnetic fluid (MF). Then, it was exposed to a magnetic field in the range of 0 to 200 mT, applied transversally to the fiber axis. An overall exponential decrease of the wavelength of the reflection spectrum with the increase of the magnetic field was obtained, with a sensitivity and resolution of 120.5 ± 4.4 pm/mT and 8.3 μT, respectively, in the range of 0 to 80 mT (linear behavior). The proposed sensor represents a cost-effective solution for the magnetic field sensing, with an improved performance compared with other devices already reported in the literature.
This work reports the development of a bioinspired sensor capable of measuring vertical and shear (tangential) forces. The sensor is composed of two materials, the polylactide (PLA) and epoxy resin, combined with a photosensitive optical fiber with two fiber Bragg gratings (FBG1 and FBG2). The FBG1 was placed in a cavity filled with epoxy resin, while FBG2 was between the cavity and the shear wall that undergoes shear force. This FBGs’ encapsulation allowed one of them to be affected by vertical and shear forces (FBG1), while FBG2 was only affected by shear force. The calibration and performance tests were carried out with the aid of an electronic tri-axial force sensor. From these tests, sensitivities of K1V= 0.02±2.35x10-4 nm/N; K1S= 0.13±3.25x10-3 nm/N; K2V= -2.88x10-4±6.72x10-5 nm/N and K2S= -1.77±0.03 nm/N to each type of force, for FBG1 and FBG2, respectively, were achieved. The obtained results demonstrated the reliability of the developed solution, with a significant improvement of its sensitivity to shear force, and a low production complexity, when compared to other previously reported optical sensors.
This work consists on the design and implementation of a compact and accurate biaxial optical fiber sensor (OFS) based on two in-line fiber Bragg gratings (FBGs) for the simultaneous measurement of shear and vertical forces. The two FBGs were inscribed in the same optical fiber and placed individually in two adjacent cavities. In the calibration and performance tests, the response from the optical fiber cells was compared with the values given by a three-axial electronic force sensor. Sensitivity values obtained for the FBG1 are K1V= (14.15±0.10) pm/N (vertical force) and K1S= (-26.02±0.08) pm/N (shear force) and for the FBG2 are K2V= (7.35±0.02) pm/N and K2S= (-24.29±0.08) pm/N. The conversion of the Bragg wavelength shift, given by the optical fiber sensors, into the shear and vertical force values is also presented along with its comparison to the values retrieved by an electronic sensor, yielding to low RMSE values, which shows the high accuracy of the algorithm applied. This work stands out from the others with optical fiber by the simplicity of its structure. The proposed solution represents a compact and reliable device for simultaneous measurement of shear and vertical forces, useful in several areas, such as: incorporation into insoles for plantar pressure and shear force measurement; electronic skin technologies; smart rehabilitation robotic exoskeletons; or even biomimetic prosthesis.
Tilted fiber Bragg gratings (TFBGs) are one of the most attractive kind of optical fiber sensor technology due to their intrinsic properties. On the other hand, the acousto-optic effect is an important, fast and accurate mechanism that can be used to change and control several properties of fiber gratings in silica and polymer optical fiber. Several all-optical devices for optical communications and sensing have been successfully designed and constructed using this effect. In this work, we present the recent results regarding the production of optical sensors, through the acousto-optic effect in TFBGs. The cladding and core modes amplitude of a TFBG can be controlled by means of the power levels from acoustic wave source. Also, the cladding modes of a TFBG can be coupled back to the core mode by launching acoustic waves. Induced bands are created on the left side of the original Bragg wavelength due to phase matching to be satisfied. The refractive index (RI) is analyzed in detail when acoustic waves are turned on using saccharose solutions with different RI from 1.33 to 1.43.
In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06 pm/N. The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons’ control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).
Optical fiber sensors has become one of the most promising sensing technologies. Within all the optical fiber sensing technologies, the Fabry-Perot interferometer (FPI) micro-cavities are one of the most attractive, due to the size, linearity and higher sensitivity. In this work we present the recent results, achieved by our group, regarding the production of optical sensors, by recycling optical fibers destroyed through the catastrophic fuse effect. This enabled the production of FPI sensors, in a cost effective way, tailored for the monitoring of several physical parameters, such as relative humidity (RH), refractive index (RI) and hydrostatic pressure.
In this work, an optical fiber hydrostatic pressure sensor based in Fabry-Perot micro-cavities is presented. These micro structures were generated by the recycling of optical fiber previously damaged by the fiber fuse effect, resulting in a cost effective solution when compared with the traditional methods used to produce similar micro-cavities. The developed sensor was tested for pressures ranging from 20.0 to 190.0 cmH2O and a sensitivity of 53.7 ± 2.6 pm/cmH2O for hydrostatic pressures below to 100 cmH2O was achieved.
Fiber Bragg grating sensors were attached to the surface of a rechargeable lithium battery in order to monitor its thermal and strain fluctuations through charge and different discharge C rates. During the discharge process above 1C, it were observed, a temperature and strain fluctuations of a 4.12 ± 0.67 °C and 24.64 ± 6.02 με, respectively. In the regular charge process, a temperature and strain variation of 1.03 ± 0.67 °C and 15.86 ± 6.02 με, were detected.
In this work, the simultaneous regeneration of seed fibre Bragg gratings (FBGs) during the diamond-grating coating and the thermal monitoring of that process is presented. The diamond was deposited through the hot filament chemical vapour deposition (HFCVD) process, and due to the high temperatures characteristics of this method (above 800 ºC), regenerated FBGs are suitable samples to be coated. The advantages of this study are the possibility to regenerate the seed gratings during the coating process, becoming the fibre more resistant and the procedure less time consuming, and to control the temperature, a critical parameter for the morphology of the deposited layers.
Injection molding is an important polymer processing method for manufacturing plastic components. In this work, the thermal monitoring of the thermoplastic injection molding is presented, since temperature is a critical parameter that influences the process features. A set of fiber Bragg gratings were multiplexed, aiming a two dimensional monitoring of the mold. The results allowed to identify the different stages of the thermoplastic molding cycle. Additionally, the data provide information about the heat transfer phenomena, an important issue for the thermoplastic injection sector, and thus for an endless number of applications that employ this type of materials.
Madeira wine is a fortified wine produced in Madeira Island, Portugal. Its characteristics are strongly influenced by the winemaking method used which includes a typical and unique step called estufagem. This process consists on heating the wine up to 55 ºC for at least 3 months. In this paper, the characterization of the sensor for the pilot scale facility of estufagem installed in Madeira University is presented, being the device an optimization of a previous version. The response of the sensor was tested towards colour and refractive index, showing a good performance. Madeira wine with different estufagem times was also analysed.
In this work, the regeneration of saturated fiber Bragg gratings during the diamond coating of the fiber is presented. Due to the high temperatures characteristic of the hot filament chemical vapor deposition (HFCVD) process (around 800 ºC), uniform fiber Bragg gratings (FBGs) are not appropriate to be coated. Nevertheless, regenerated Bragg gratings are a suitable solution for this drawback. Its production process involves the inscription of a saturated FBG followed by a time consuming heat treatment. Here it is proposed to take advantage of the high temperatures characteristic of the HFCVD process to simultaneous regenerate the grating and coat the fiber with diamond.
In the last decades the fiber Bragg gratings (FBG) and Fabry-Perot Interferometer (FPI) micro cavities based sensors have become one of the most attractive optical fiber sensing technologies. However, its production requires a significant economical investment. We propose a cost effective solution based on micro cavity generated by the recycling of optical fibers destroyed through the catastrophic fuse effect. This technique considerably reduces the experimental complexity and the production costs. In this paper, the application of these sensors in the monitoring of several parameters, such as refractive index, pressure, strain and temperature is presented.
Currently, the surface plasmon resonance (SPR) based sensors are mainly focused in visible frequencies, being a barrier for a better integration with the typical fiber optical communication transmission bands. Here, it is presented a theoretical analysis of a SPR based fiber optic sensor with a uniform gold coating on a U-shaped probe. The sensor does not require any fiber etching treatment which eases and improves the control of the overall process. The response of the device to refractive index variations was investigated and a resolution of 10-8 is foreseen for refractive indices around 1.413, becoming the proposed sensor a useful tool for biological and chemical applications.
In this work we present a cost effective strain sensor based on micro-cavities produced through the re-use of optical fibers destroyed by the catastrophic fuse effect. The strain sensor estimated sensitivity is 2.22 ±0.08 pm/μƐ. After the fuse effect, the damaged fiber becomes useless and, consequently, it is an economical solution for sensing proposes, when compared with the cavities produced using other complex methods. Also, the low thermal sensitivity is of great interest in several practical applications, allowing eluding cross-sensitivity with less instrumentation, and consequently less cost.
In this work, the study of a particular step of Madeira’s winemaking process called estufagem with a plastic optical fibre sensor is presented. Madeira wine is a type of fortified wine produced in the Madeira island of Portugal. The characteristic aroma and exceptional stability of these wines result from the singular used winemaking method that consists in the estufagem where the wine is heated up to 55 °C for at least 3 months, among other steps. This heating based process can produce significant changes in wine colour, aroma and taste. By measuring the transmitted optical power through the wine in three different cells at three different wavelengths it is possible to monitor wine colour evolution during the estufagem. The plastic optical fibres offer easy non-skilled handling, ruggedness and low cost, overcoming the difficulties of the electronic and conventional systems and improving the time of the laboratory offline methods. Results show that it is possible to distinguish the different Madeira wines (from sweet to dry wines) obtained based on different wine grapes as well as the colour evolution during the diverse months of the estufagem.
In this work, Bragg gratings were used to monitor, in real time, the temperature during the diamond deposition process obtained by hot filament chemical vapor deposition (HFCVD). Due to the instability of uniform fiber Bragg gratings (FBGs) to high temperatures, regenerated fiber Bragg gratings (RFBGs) were utilized. The results reveal that the diamond deposition process occurs at about 832 ºC (in the experimental conditions used in this case). The work also suggests that RFBGs are suitable devices to monitor processes which, as in the diamond deposition, the temperature is a critical parameter, and where other traditional methods have a little feasibility due to the own experimental setup or samples type under study.
The present work addresses the need for new devices felt in the context of quality control, especially in the food industry. Due to the spectral dependence of the attenuation coefficient, a novel dual-parameter sensor for colour and refractive index was developed and tested. The sensor employs plastic optical fibres to measure the transmitted optical power in three measurement cells each with a different incident wavelength. The performance of the sensor was tested using several dyes at different concentrations and aqueous solutions of glycerine and ethanol. Results show that this technique allows the monitoring of refractive index and colour without cross-sensitivity.
The arterial stiffness evaluation is largely reported as an independent predictor of cardiovascular diseases. The central pulse waveform can provide important data about arterial health and has been studied in patients with several pathologies, such as diabetes mellitus, coronary artery disease and hypertension. The implementation and feasibility studies of a fiber Bragg grating probe for noninvasive monitoring of the carotid pulse are described based on fiber Bragg grating technology. Assessment tests were carried out in carotids of different volunteers and it was possible to detect the carotid pulse waveform in all subjects. In one of the subjects, the sensor was also tested in terms of repeatability. Although further tests will be required for clinical investigation, the first studies suggest that the developed sensor can be a valid alternative to electromechanical tonometers.
In this paper, the coating of optical Bragg gratings with nanocrystalline diamond, obtained by hot filament chemical
vapor deposition (HFCVD), is described. Due to the high temperature coating process, uniform fiber Bragg gratings
(FBG) were erased during the diamond deposition. However, in the case of regenerated fiber Bragg gratings (RFBG),
although attenuated, the optical signal is maintained. The results of the thermal and mechanical characterization of
diamond coated RFBG (D-RFBG) suggest that they may be an important tool in the sensing field, including monitoring
of high temperatures under harsh environments.
One of the early predictors of cardiovascular diseases, with growing interest, is the arterial stiffness which is typically
evaluated through the velocity and morphology of the arterial pressure wave.
In each cardiac cycle the heart generates a pressure wave which propagates through the arterial tree. Along its path, the
pressure wave interacts with the arterial walls and, consequently, the morphology of a local arterial pressure wave can be
assessed by the arterial distention movement. Due to its superficiality, proximity of the heart and high probability of
atherosclerosis development, the carotid artery has particular interest to be monitored.
In this work, the development of a non-invasive fibre Bragg grating (FBG) probe for the acquisition of the arterial
distention wave is presented. Comparing to traditional methods, optical FBG based sensors can offer many advantages,
namely, compactness, immunity to electromagnetic interference, high sensitivity, low noise and immunity to light source
intensity due to its codification in the wavelength domain.
The arterial movements induce strain on a uniform FBG, with the arterial distention pattern. The carotid pulse wave was
successful accessed in young human carotid artery, with an acquisition rate of 950 Hz, allowing a clear distinction of the
carotid pulse identification points.
Sensors based on side-polished plastic optical fibre are presented. To enhance the sensitivity to a certain physical
parameter, the guiding properties of an optical fibre have to be weakened. Side-polishing technique offers a simple
implementation, since the mechanical resistance of the POF allows an easy removal of a portion of the jacket, cladding
and core. Three sensors are characterized under a wide range of external refractive indexes. Both, theoretical and
experimental results show that the range of operation of the refractive index sensor can be shifted by using different
geometries or different macrobending conditions of the sensitive area. The phenomenon behind the principle of operation
of the sensor is the reflection and transmission of light at an interface of two dielectric media expressed by Fresnel's
equations. The use of this intrinsic scheme to monitor the cure process of a material or the viscosity of a liquid is also
presented. The changes in refractive index are used to monitor, in real time, the cure of different materials such as resins
and varnishes because the optical properties of the material can be related to the density of the material. The viscosity of
a liquid is related to the droplet formation in a convexly bended sensor.
Optical device based on a tilted fibre Bragg grating (TFBG) to perform simultaneous measurement of refractive index
(RI) and temperature is proposed. Using two different demodulating techniques, namely monitoring the core mode
wavelength and the area of the transmission spectrum, it is possible to measure, separately, temperature and RI,
respectively. The proposed method uses a grating, which does not require a reduced diameter, and a single measurement
equipment. Measurements with resolution up to 5.7 x 10-4 and 0.5 °C were achieved, for RI and temperature,
respectively. Theoretically, the resolution of RI measurements can go as bellow as 2 x 10-5.
In this work, we present a simple approach to design a multichannel sampled fiber Bragg grating (SFBG) for dispersion
compensation, based on groups of SFBG with phase modulation between groups. We present also an apodization
technique that minimizes the high group delay ripple that occurs with this approach. This design can be implemented
with a uniform phase mask and a low resolution positioning device.
This paper presents a comparative study of the behaviour of different kinds of optical fibre sensors in response to high
temperatures. It compares the performance of regenerated fibre Bragg gratings (FBGs) written in hydrogen-loaded and
non-loaded fibres with long period gratings (LPGs) written through the two different processes of ultraviolet (UV)
irradiation and electrical arc discharges. This work shows the importance of the use of hydrogen-loaded fibres to achieve
regenerated FBGs capable of withstanding high temperatures as high as 955°C. In addition, the results demonstrated that
LPGs recorded by electric arc discharges have higher thermal resistance than LPGs written by UV radiation.
A sensor for simultaneous measurements of strain, temperature and refractive index (RI) is proposed. The device is based
on a single 8º tilted fiber Bragg grating (TFBG). Monitoring the core mode and ghost mode wavelength, it is possible to
discriminate strain and temperature. The RI measurement is obtained through computation of the transmission spectrum
area. Resolutions up to 4 με, 3.1 ºC and 5.7 x10-4 were achieved. The present sensor can be an important tool in the
sensing field.
°In this work, a dual sensor for simultaneous measurements of strain and refractive index (RI) is proposed. The sensor is
based on a 4.5 tilted fibre Bragg grating (TFBG). Using two different demodulating techniques, namely monitoring the
core mode wavelength and the normalized area of the transmission spectrum, it is possible to measure, strain and RI with
a resolution of 2.5 με and 3 x 10-5, respectively.
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